(1) Field of the Invention
The present invention relates, in general, to ink jet printers. More particularly, the present invention relates to multinozzle ink jet printers wherein a characteristic of the print head is controlled so that the quality of prints generated from the head is optimized.
(2) Prior Art
The use of ink jet printers for printing data and other information on a strip of recording media is well known in the prior art. One type of conventional ink jet printer incorporates a plurality of electrical components and fluidic components. The components coact to enable the printing function. The fluidic components include a print head having a chamber for storing a printing fluid or ink and a nozzle plate with one or more ink nozzles interconnected to the chamber. A gutter assembly is positioned downstream from the nozzle plate in the flight path of ink droplets. The gutter assembly catches ink droplets which are not needed for printing on the recording medium.
In order to create the ink droplets, a drop generator is associated with the print head. The drop generator produces a perturbation at a frequency which forces thread-like streams of ink, which are initially ejected from the nozzles, under pressure to be broken up into a series of ink droplets at a point (called the break-off point) within the vicinity of the nozzle plate.
A charge electrode is positioned along the flight path of the ink droplets. Preferably, the charge electrode is positioned at the break-off point of the ink droplets. The function of the charge electrode is to selectively charge the ink droplets as said droplets break off in proximity to said electrodes. A pair of deflection plates is positioned downstream from the charge electrodes. The function of the deflection plates is to deflect a charged ink droplet either into the gutter or onto the recording media.
Another type of conventional ink jet printer incorporates a plurality of magnetic components and fluidic components. The fluidic components are substantially equivalent to the fluidic components previously described. However, the electrical components are replaced with magnetic components for influencing the direction of travel of the droplet streams. This type of ink jet printer is well known in the prior art and, therefore, the details will not be described.
One of the problems associated with ink jet printers of the aforementioned types, is the generation of "satellite droplets." The satellite droplets are usually smaller in size than the droplets used for printing (hereinafter called print droplets) and are usually interspersed therewith. Although the print droplets can be controlled electrically or magnetically so as to reproduce copies with acceptable print quality, it is extremely difficult, if not impossible, to control the satellite droplets.
In the first instance, the satellite droplets tend to merge with the print droplets. The newly formed droplets (that is the print droplets plus the satellite droplets) usually have different charge to mass ratios. Also, the newly formed droplets (hereinafter called merged droplets) tend to travel at a different velocity than the normal print droplets. As was stated previously, printing is done by the droplets propelled in a controlled manner to impinge on the support medium. When a mixture of merged droplets and normal print droplets are propelled towards the support medium, the nonuniform properties of the droplets cause inaccurate placement of the droplets on the recording media. This inaccurate drop placement results in poor print quality.
Even when the satellite droplets do not merge with the print droplets, they tend to assume an independent flight path. The alternate result is that the satellite droplets either impinge the recording medium randomly (that is at the wrong position) or impinge the components positioned around the flight path of the droplets. Where the satellite droplets impact the recording media at the wrong position, the print quality is poor. Similarly, where the satellite droplets impinge on the components, the reliability of the ink jet print system is reduced since the droplets wet the electrical components resulting in an electrical short circuit.